1. The Field of the Invention
The present invention relates to methods for immobilizing aryl-containing organic ligands on a support material. The organic ligands are immobilized using a tethering agent that is bonded to the aryl group and to a support material.
2. The Relevant Technology
Catalysts are widely used in the manufacturing of organic compounds such as pharmaceuticals, agrochemicals, flavors, fragrances, and other functional materials. Catalysts can be generally divided into two main types, homogeneous and heterogeneous. Homogeneous catalysts are catalysts which are in the same phase as the reactants and/or products during the chemical reaction. Heterogeneous catalysts are catalysts that are not in the same phase as the reactants and/or products during the chemical reaction.
Homogeneous reactions are typically carried out in a liquid solution with a catalyst that is soluble in a liquid reaction medium. A catalyst dissolved in liquid phase reactants and products can be advantageous for achieving good selectivity and activity. In contrast, heterogeneous reactions are typically carried out in a liquid reaction medium, but the heterogeneous catalyst is typically in a solid phase. Heterogeneous catalysts can be separated from the liquid phase using separation techniques such as filtration or centrifugation.
Homogeneous catalysts are important in the pharmaceutical and fine chemicals industries where there is a growing need for catalysts that meet special selectivity requirements. Recently there has been an increased need for chiral selectivity to produce single enantiomer products. The need for single enantiomers is particularly important for pharmaceuticals where one enantiomer may have a beneficial pharmacological effect and another enantiomer of the same compound may have an undesirable side effect. Even when one enantiomer is not known to cause adverse affects, manufacturing a single enantiomer can be advantageous to simply avoid the expense of clinical trials on both enantiomers.
Historically, homogeneous catalysts, especially soluble organometallic complexes (metal-ligand complexes), have proven to be the most effective in achieving chiral selectivity. The challenge with using homogeneous catalysts is to remove the catalyst from the final product. Catalysts that are soluble in the same phase as the product can be difficult to separate from the product since the two species will be intimately mixed. Homogeneous catalysts that remain in the final product are often a source of contamination and reduce the quality of the final product. On the other hand, simply attaching a homogeneous catalyst to a support is not feasible, as it may de-activate the catalyst or interfere with the desired catalytic activity (e.g., by altering a desired conformation of the ligand as a result of a portion of the ligand being bound or attached to the solid support, and/or as a result of steric hindrance).